In recent years, demands for an increase in information recording density on an optical disk recording/reproducing device (to be referred to as an “optical disk apparatus” unless otherwise noted hereinafter) using a phase change recording medium, a pigmentary change recording medium, a magneto-optical recording medium, an optical recording medium (to be referred to as an “optical disk” unless otherwise noted hereinafter) such as a read-only medium on which data is recorded in advance with concavo-convex or the like, an increase in density of pixels on an electronic imaging device such as a CCD (imaging element), a liquid crystal panel, or an organic EL panel, and an increase in miniaturization rate and integration density on a semiconductor integrated circuit have been high. From this background, efforts to miniaturize devices such as the optical disk apparatus, the electronic imaging device, and the semiconductor circuit to achieve higher integration are actively made.
However, with the advance of miniaturization of these devices, important technical problems have arisen for realizing integration higher than conventional integration by detecting and removing a foreign body such as a stain, dust, an oil film, or a scratch. In manufacturing or use of a product, a foreign body adhering to the device causes a decrease in manufacturing yield or product performance. For this reason, accurate detection of a foreign body has become important.
In particular, in the optical disk apparatus, a foreign body adhering to the surface of an optical disk is a disincentive factor of an increase in information recording density. More specifically, in the case where recording marks are reduced in size by using a short-wavelength light source such as a blue laser to increase a recording bit density, when even a foreign body which does not cause any problem on a compact disk adheres to an optical path of a light beam, the following problem arises. Therefore, the optical disk apparatus having a high information recording density cannot be easily put into practical use.
When a light beam is irradiated on a recording layer of an optical disk to form recording marks on the recording layer, the light beam is affected by light shielding, refraction, reflection, or the like depending on the optical characteristics of a foreign body adhering to the optical disk surface to cause the positions and sizes of the recording marks to vary. The influence of the variations increases as a light beam spot diameter and a recording mark length decrease. Thus, recording marks having high reliability and a high information recording density cannot be easily formed at high accuracy.
When a light beam is irradiated on the recording layer and the track layer of a phase change recording medium or a pigmentary change recording medium to read recording marks, the light beam is similarly affected by light shielding, refraction, reflection, or the like depending on the optical characteristics of a foreign body adhering to the surface of the optical disk, and thus, the recording marks and tracks cannot be correctly read. As the recording marks and tracking pitches are decreased in size, the influence of the foreign body increases. Therefore, recording marks having a high information recording density cannot be easily read at high accuracy.
The optical disk apparatus is expected to be developed in a new market as a large-capacity recording device with a small size, a light weight, and a low price. However, an optical disk apparatus with an increased capacity by increasing an information recording density has poor recording/reproducing reliability against a foreign body. Thus, when the optical disk apparatus is mounted on an apparatus or a system such as a computer apparatus, a computer system, a computer network system, a vehicle such as an automobile, a train, a ship, or an airplane, and an image complex apparatus such as an MFP (Multi-Function Product) which require recording/reproducing reliability, the reliabilities of the apparatuses and the systems are disadvantageously deteriorated.
In order to solve the above problem, an optical disk apparatus having a means for detecting a foreign body adhering to the surface of an optical disk is conventionally proposed.
FIG. 34 shows an example of such an optical disk apparatus, and is a schematic view of a stain detection device for an optical disk disclosed in a patent document JP6-223384A. A light radiated from a semiconductor laser light source 5 is converged on the surface of an optical disk 100 through an object lens 7, and the reflected light is received by a light-receiving element 53 having two divided regions A and B through a ¼ wavelength plate 51 and a polarized beam splitter 6. The light intensities of the lights received in the regions A and B are converted into voltages through I-V conversion circuits 54a and 54b, and the voltages in the regions A and B are added to each other by a sum signal reproducing circuit 55 to generate a sum signal voltage. On the other hand, the sum signal voltage calculated from the theoretical reflectance of the optical disk is set as a reference voltage of the optical disk which is free from stain. The sum signal voltage is compared with the reference voltage. When the sum signal voltage is lower than the reference signal voltage, a warning is given, or the operation is stopped.